There has always been a need to accurately and automatically measure the level of particulate or other bulk materials such as sand while they are being maintained in various bins or containers. This is desirable not only to know precisely to what degree the container is filled, but furthermore so that appropriate actions, such as refilling or terminating the filling of the container, can be taken where necessary.
It was determined at quite an early stage that merely calculating the amount of material added or substracted from a container was highly inadequate and imprecise in determining such levels. Thus, the use of various sensors, whether electrical, pneumatic, or otherwise, was developed so that a more precise reading of the level of such materials could be determined within such containers, whether they are open or closed containers.
As an example, U.S. Pat. No. 3,734,313 to Gauthier et al, assigned to Donald Engineering Company, Inc., discloses a level indicator which includes a pair of tubes coupled to a source of pressurized gas, as can be seen in FIG. 1 thereof. The two tubes, including an upper tube and a lower tube, are J-shaped, and each includes an air gap 27 between its upwardly directed exit nozzle and an input tube 28 thereabove. Thus, when the particulate material in the container reaches either of the two levels at which the specific air gaps are located it fills that gap and prevents the air from flowing therebetween, thus increasing the pressure drop therein. Such a device, however, is not only quite complex, but also only provides information as to specific levels, i.e., one in connection with each such device, and a constant indication of the precise level in the container cannot be effected with such a device.
Other devices employ collapsible diaphragms mounted within the containers or storage bins which are collapsed by the weight of the particulate material at a given location so as to provide a level indication therein. These include U.S. Pat. No. 3,994,169 to Wolford, which discloses such a device having an elongated sensor or diaphragm member running the length of the container so that the displacement of air within the diaphragm can be measured whenever it is desired to determine the level of material therein. Again, aside from the question of the accuracy of this device continuous measurements are not obtained therewith. Similarly, U.S. Pat. No. 3,290,938 to Miller also discloses a device which includes a diaphragm or tube 16 also disposed within a container, so that as material is included in the container more of the tube collapses against the pressure of the particulate material, thereby in turn displacing air from the diaphragm into a bellows which can be read directly on indicator 38. This device again does not provide the type of accuracy which is desired in many instances.
Another type of measuring device is shown in U.S. Pat. Nos. 3,213,670 to MacGeorge and 3,459,035 to Russon. In each of these patents a single sensor is disposed above the level of material in the container to project a gaseous stream such as air against the upper level of the material and to thereby sense the air pressure reflected back to the sensor. In the device shown in the 3,213,670 patent, it is thus necessary to continuously adjust the level of the probe above the liquid level to maintain it at a predetermined distance thereabove, and in the 3,459,035 patent the probe 10 maintains its position, and the probe is actuated only when the level of material in the container reaches a desired level adjacent its end.
Finally, a number of additional such devices include a plurality of pressure sensors mounted at different heights in a storage chamber or bin for such measuring purposes. These include U.S. Pat. No. 2,696,606 to De La Pomelie, assigned to Gaz de France Service National, and U.S. Pat. No. 3,971,254 to Sherman, assigned to Kamyr, Inc.
The search has therefore continued for such a pressure measurement device which is simple in construction, and which can continuously monitor the precise level of material within a container or bin.